Antioxidant activity of ethanolic extract of fruits of Terminalia chebula (500 mg/kg body wt, orally for 30 days) against isoproterenol-induced oxidative stress was investigated in rats. The levels of serum lipid peroxides, iron, ascorbic acid, vitamin E, plasma iron-binding capacity, and the activities of ceruloplasmin and glutathione were assayed, in addition to the activities of the antioxidant enzymes - glutathione peroxidase, glutathione reductase, glutathione-S-transferase, superoxide dismutase and catalase in the heart tissue. Administration of isoproterenol increased the levels of lipid peroxides and iron, with corresponding decrease in the activities of the enzymic and nonenzymic antioxidants. The pre-treatment with ethanolic extract of fruits significantly prevented the alterations induced by isoproterenol, and maintained a near normal antioxidant status. Results suggest that the cardioprotective effect of T. chebula fruit may partly be attributed to its antioxidant properties.